The present invention relates to a holding tube for a heat treatment plant using injection heating, comprising a first, fixed section consisting of a conduit of a predetermined length, and also a constant counter pressure valve.
The heat treatment of food products for extended shelf life is a well-known and often employed method. The food products may, for example, consist of various dairy products such as milk, cream or yoghurt.
The heat treatment may be put into effect in a plurality of different ways, directly or indirectly. Indirect methods are, for example, heating by means of different types of heat exchangers. There are two main types of direct methods, injection and infusion, where heating takes place by means of steam. By employing a direct method, an extremely rapid heating will be obtained. Rapid heating is, today, desirable when a product of long shelf life is sought for at the same time as the intention is to obtain a product with improved flavour properties. The rapid heating permits heating to elevated temperatures for brief periods of time, which reduces thermal stresses on the product and thereby reduces the risk of overtreatment.
The present invention relates to heating by means of injection. Today, injection is a common heating method in commercial heat treatment plants which employ direct heating.
Heating by injection implies that the product, for example milk, is preheated to approx. 80xc2x0 C. and pressurised. The product enters, together with superheated steam, into an injector and is there intermingled, normally with the aid of annular, concentric nozzles. The steam is condensed and heat is transferred to the product which, by such means, is very rapidly heated to the desired temperature.
All modem heat treatments of food products have for their purpose, on the one hand, to heat the product to a certain predetermined temperature, and, on the other hand, to keep the product at this temperature for a certain, predetermined period of time. During this time interval, the product stays in a so-called holding tube. By selecting different temperatures and different stay times, products will be obtained which are aseptic or which have extended shelf life.
For heat treatment plants using injection heating, use is made of separate holding tubes which may consist of a helical conduit of a predetermined length or a section of straight conduit of a predetermined length. Alternatively, the holding tube may consist of a combination of helical and straight conduit.
Regardless of the design of such holding tubes, they cannot be adjusted. The capacity for which the heat treatment plantxe2x80x94and thereby also the holding tubexe2x80x94is calculated normally corresponds to a number of filling machines for packing the product in consumer packages. When one or more of these filling machines possibly drops out of operation because of some operational stoppage, the flow is reduced and there rapidly occurs an overly long stay time in the holding tube, with the result that the product becomes overtreated. It is therefore desirable in the art that the holding tube may rapidly be adjusted so that the stay time can be kept constant. Also when the intention is to be able rapidly to vary production to meet different foods which require different stay times, use may be made of an adjustable holding tube. Without such a possibility of varying the stay time, the plant must be rebuilt or alternatively an overtreated product must be tolerated.
A variable holding tube is disclosed in Swedish Patent Specification SE 510797. This holding tube has one or more cooled sections which may be stepwise coupled in when necessary. A disadvantage inherent in this holding tube is that the steps by which the holding tube may be reduced are fixed, and, in certain applications, the steps may be too large.
One object of the present invention is to design a holding tube which is steplessly adjustable and which gives a reliable and defined stay volume for the product.
A further object of the present invention is that the holding tube is to be simple and economical to manufacture and may be washed in a satisfactory manner together with the remaining equipment in the plant.
These and other objects have been attained according to the present invention in that the holding tube of the type described by way of introduction has been given the characterising feature that the holding tube also includes a second, adjustable section consisting of a cyclone and an inclining conduit of a predetermined length, as well as a device disposed to maintain a defined liquid level in the conduit.
Preferred embodiments of the present invention have further been given the characterising features as set forth in the appended subclaims.